Fluoropolymers exhibit unique properties that are not observed with other organic polymers. Fluoropolymers possess high thermal stability, chemical inertness, low flammability, low coefficient of friction, low surface energy, low dielectric constant, weather resistance, and gas barrier properties. These fluoropolymer properties enable their use in aerospace, automotive, construction, medical, pharmaceutical, and semiconductor industries. However, fluoropolymers have various drawbacks. As homopolymers, fluoropolymers are often highly crystalline, which induces poor solubility in common organic solvents and gives fluoropolymers relatively high melting points. Further, fluoropolymers do not adhere strongly to most surfaces and are known for their non-stick characteristics. As such, processing of fluoropolymers is difficult because of the lack of solubility in the common organic solvent that are typically used to apply polymers to various substrates, high melting points that results in application temperatures that may harm the substrate to which they are applied, and lack of adhesion to common substrates.
Some fluoropolymers derived from fluoromonomers and functional hydrocarbon monomers are known in the art and have been found to combine the properties of both the fluorine-containing polymers and the properties of the functional hydrocarbon monomers. Such materials can be used as barrier materials, chemical sensors, and ion-exchange and gas separation membranes. There are three principal ways to synthesize fluoropolymers that bear functional groups: (a) homopolymerization of functionalized fluoromonomers, (b) copolymerization of fluoroolefins with functional monomers, and (c) modification of common fluoropolymers by graft and block copolymerization with functional monomers. Chemical modification of common fluoropolymers is also possible. Because of their limited solubility and chemical inertness, however, there is a very limited range of reagents that can affect fluoropolymers, and only a very limited number of functional groups can be incorporated with fluoropolymers in this manner. Further, homopolymerization of functionalized fluoromonomers is very limited due to the difficulty in synthesis and high cost of functional fluoromonomers.
By way of example, U.S. Pat. No. 2,392,378 discloses copolymerization of CTFE with ethylene. Tabata et al. (J. Macromol. Sci. Part A 1970, 4, 801) investigated the kinetics of radical copolymerization of CTFE with ethylene, propylene, and isobutylene. U.S. Pat. No. 5,258,447 claims copolymerization of CTFE and 2-hydroxyethyl allyl ether with an unsaturated carboxylic acid ester as a third monomer. A CTFE and vinylidene chloride (“VDC”) copolymer coating used to develop electrostatographic images is reported in JP 02203356 A. Copolymers of CTFE-VDC are reported as release and fluxing agents in JP 52121063 A and U.S. Pat. No. 2,944,997, respectively. A terpolymer including CTFE, vinylidene fluoride, and another fluoroolefin is disclosed in U.S. Pat. No. 3,053,818.
As noted above, fluoropolymers often find application in the pharmaceutical industry, particularly in pharmaceutical packaging application. Selecting a packaging material for a drug is critical for a successful market launch. Packaging components must meet functional requirements to help protect the purity of the product for its shelf-life, and the packaged drug can be harmed if the packaging components are not compatible with the drug. Given that many active pharmaceutical ingredients (API) and excipients in drug formulations are sensitive to their environment, there is a growing need for packaging materials with varying levels of moisture and oxygen barrier properties.
Currently, the “mid-barrier” segment, which focuses on materials with a water vapor transmission rate of about 0.3 to about 0.8 grams/mil/m2-day, is serviced by polyvinylidene chloride (“PVDC”)-coated polyvinyl chloride (“PVC”) packaging films. Although PVDC films meet most of the critical needs in drug packaging requiring mid-barrier, they are brittle, become yellow upon exposure to light, and release gas that corrodes the tooling during processing.
Polychlorotrifluoroethylene (“PCTFE”) film is also used in mid-barrier pharmaceutical and medical packaging. It is optically transparent, chemically inert, nonflammable, and plasticizer- and stabilizer-free. Its superior moisture barrier properties enable worldwide distribution of pharmaceuticals to all climates and environments including Zone 4-tropical locations. Further, PCTFE films laminate well with a wide variety of substrates and thermoform well with conventional blister packaging equipment. To date, demand for packaging materials with varying moisture barrier levels has been met primarily with PCTFE films of different thicknesses. For example, PCTFE films are available in a range from 15 microns to 150 microns. While these varying thickness materials may satisfy the barrier needs, they are not cost effective and their use is restricted to specialty packaging applications. Also, thinner films are difficult to extrude. One typical way to reduce the cost of a packaging material fabricated from a costly polymer is to form multilayer structures in which the polymer film is laminated with other, less costly polymer films. As noted above, however, fluoropolymers do not adhere strongly to most other polymers. This property is disadvantageous because poor bond strength between layers can result in the delamination of multilayer films. As a result, specialized intermediate adhesive layers that increase the cost of the packing structure are generally needed to attach most other polymer films to fluoropolymer films.
Thus, there remains a need in the art for protective barrier films that are clear and stable, exhibit good moisture barrier properties, thermoform easily using existing processing equipment, and are able to adhere to other polymers. Further, there remains a need in the art for cost effective packaging films having the moisture barrier properties that meet present and future performance demands. Still further, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.